Old English leof "dear, valued, beloved, pleasant;" also as a noun, "a beloved person, friend," from Proto-Germanic *leubo- (cf. Old Norse ljutr, Old Frisian liaf, Dutch lief, Old High German liob, German lieb, Gothic liufs "dear, beloved"), from PIE root *leubh- "love" (see love (n.)). As an adverb, "dearly, willingly" from c.1250. I want and I'd love to are overworked and misused to fill the hole left in the language when I would lief faded in 17c.